Connectors for use in the connection of electrical circuits in automobile need to exhibit a high oil resistance as well as high waterproof sealing properties. Most sealing rubber parts to be mounted on these connectors, such as packing and rubber stopper, are made of oil-bleeding rubber material. In such a use, as molding materials there are used an oil-bleeding NBR obtained by blending a butadiene-acrylonitrile copolymer with an aliphatic hydrocarbon oil (JP-A-61-21177 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")), oil-bleeding silicone rubber obtained by blending a silicone rubber with a silicone oil (JP-A-62-252457), oil-bleeding polyolefin rubber obtained by blending a polyolefinic rubber with an ester plasticizer (JP-A-63-309542), etc.
However, all these rubber materials have defects. For example, NBR materials are disadvantageous in that they are not heat-resistant enough to use in high temperature zones in automobile engine room, though being available at a low price and excellent in oil resistance. Silicone rubber materials are excellent in heat resistance, low-temperature resistance and oil resistance but are expensive and find difficulty in general-purpose properties. Further, polyolefinic materials have an insufficient oil resistance and thus are not suitable for use in automobile engine room.
Under these circumstances, it is impossible to reduce the price of the silicone rubber having relatively excellent properties while maintaining the excellent properties. Therefore, various approaches for reducing the molding time of rubber parts have been proposed to reduce the price of the rubber parts. A general millable silicone rubber composition comprises an organic peroxide as a vulcanizing agent and is thus advantageous in that the blend exhibits a good storage stability and a long pot life, and can be easily handled. On the contrary, this type of silicone rubber composition is disadvantageous in that it requires a prolonged vulcanizing time and thus cannot be molded in a reduced period of time.
On the other hand, a binary liquid silicone rubber composition which undergoes addition reaction for vulcanization in the presence of a platinum catalyst has been developed. The addition reaction type liquid silicone rubber composition requires a drastically reduced vulcanizing time and thus can be molded in a reduced period of time. However, this type of liquid silicone rubber composition is disadvantageous in that the mixture of two liquids must be immediately injected into the mold, requiring an additional molding apparatus and giving troublesome operation.